RELATIONS OF THE COCCACE/E 33 



Planococcus and Planosarcina, for the motile forms, and 

 these five genera form the basis of his detailed sys- 

 tematic treatment of the group (Migula, 1900). Chester 

 (1901) accepted Migula's classification in its general out- 

 line. 



Planococcus and Planosarcina, the genera character- 

 ized by motility, are based on three or four exceptional 

 strains of cocci which differ from related forms in the 

 possession of this single property. Streptococcus, Micro- 

 coccus, and Sarcina on the other hand are large and 

 unwieldy genera. They are commonly defined by mor- 

 phological characters alone, all chain-forming cocci being 

 placed in the genus Streptococcus, all packet-forming 

 cocci in the genus Sarcina, and the rest in the great group 

 Micrococcus. In the latter genus widely dissimilar forms, 

 of diverse habit and various characteristics, have natu- 

 rally accumulated. 



The inclusion of so many species under three large 

 genera renders some grouping of the specific forms 

 within the genus an absolute necessity. No attempt 

 has been made by most observers, however, to distinguish 

 natural groups. The general plan adopted has been 

 an arbitrary division of the genera by certain salient 

 single characters, — a scheme resembling the analytical 

 keys used as a supplement to true classification among 

 the higher plants. Thus Fliigge (1886) described 44 

 species of micrococci and grouped them, first, according 

 to gelatin liquefaction and, second, according to the 



